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We pulled the 2.5 w/AX5 out of my sons 94 YJ, and put in a 4.0 w/AX15.
Does anyone know if the stock ECM will work or do we need one for a 4.0
The engine , trans and harness are out of a 95 YJ. Also there is no part of
the {new] harness that goes back to trans or t-case, There is however
a plug on it, in that general area with 10 wires going to it, the same amount of wires that the old harness has in the bundle that heads toward the rear.
I have to check and see if the colors match up or not. Maybe in 95 they went to a 2-piece harness ? Any advise would be helpfull, thanks
 

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You need a 4.0 ECM. Get one close the the year of your YJ - should be plug and play - and all your under dash stuff should still work fine. You may even get by with a 4.0 ECM out of an XJ or ZJ. I am running a 97 XJ 4.0 ECM in my 97 TJ that originally was a 2.5 with no issues at all. Verify if the ECM was equipped with any security crap though first - if it was, it wont work in your YJ. I cant help you n the wiring harness issue , not familiar with the YJs specifically. But - there should be a harness to the speed sensor at a minimum. Go to alldatadiy.com. For about $19 I think it is - you can subscribe and get basically a factory service manual online for your specific vehicle - with excellent wiring diagrams and pin out diagrams of all connectors. You may need to get one for a 94 YJ AND a 95 YJ in case there are any differences - then you can compare and maybe fabricate what you need.
 
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